1. Field of the Invention
The present invention relates to a substrate capable of mounting thereon optical components and electric circuit components together, as well as a method for making same.
The terminology "optical component or components" as referred to herein indicates one or plural optical element mounted on or received in a suitable structural member, the optical element or elements functioning to change or control the intensity, wavelength, phase, polarized state, beam shape or direction of light which has been propagated through a medium (e.g. glass or air). As examples of such optical elements are mentioned lens, prism, mirror and optical fiber.
2. Description of the Background Art
Because of the advantage of optical fiber as a transmission path, the optical communication and optical transmission technique has come to be used in various fields. For example, in a general optical communication system, the transmitter side transmits light which has been subjected to intensity modulation on the basis of transmission information (electric signal), while the receiver side detects the transmitted light signal directly and reproduces the original transmission information. In such an optical transmission system, an electric circuit for processing the electric signal on the transmitter or receiver side or in a repeater section is an essential component and it is necessary to prevent the deterioration of the frequency band characteristic which is attributable to the wiring form, etc.
According to the prior art, an electro-optical converting section on the transmitter side has been constituted, for example, as shown in FIG. 1, in which a photosemiconductor sealed-device part 1 with a photosemiconductor device such as LD (laser diode) or LED(light emitting diode) sealed in a package is fixedly held in a predetermined positional relation to a first lens 2, an optical isolator 3, a second lens 4 and a fiber assembly 5 to form a photosemiconductor module 6, which module 6 is electrically connected to a drive circuit 7. The reason why the photosemiconductor sealed-device 1 and optical components such as lenses, optical isolator, etc. are combined as a module is that, particularly in the case where the light transmission path is a single mode fiber, it is necessary to set a relative positional relation of the components with an accuracy of within 1 .mu.m.
In the above structure, however, a limit is encountered in shortening the wiring between a drive circuit which constitutes the electric circuit and the photosemiconductor sealed-device, so there has been a problem that restriction is imposed on the frequency band characteristic. Another problem is that the device becomes larger in size because it is necessary to constitute the drive circuit portion and the photosemiconductor module separately from each other.
In view of the above problems there has been proposed such a structure as shown in FIG. 2. On an insulating substrate 10 there are formed wiring patterns 11 capable of making connection between a photosemiconductor device and a driving or amplifying circuit for the photosemiconductor device. Further, a fiber assembly 13 is fixed onto the insulating substrate 10 directly with an adhesive or by soldering through a metallic pattern 12 formed in the same manner as the wiring patterns 11 as shown in the figure. For example, the fiber assembly 13 as an optical component is constituted by inserting and fixing a ferrule 15 with an optical fiber 14 inserted and fixed therein into a cylindrical housing 17 with a lens 16 press-fitted therein. The lens 16 as an optical element functions to change the shape of light beam emitted from an emission end of the optical fiber 14 serving as a light guiding optical element and radiated into the air, into a collimated beam for example.
In the prior art shown in FIG. 2, however, there is a problem that the reliability is low in the case of fixing the fiber assembly as an optical component directly onto the insulating substrate using an adhesive, while in the case of fixing it onto the metallic pattern by soldering there has been a problem that the optical coupling efficiency changes with the lapse of time due to creeping of the soldered portion over a long period.
Accordingly, it is an object of the present invention to provide a substrate for mounting optical components and electric circuit components thereon which substrate overcomes the above-mentioned problems of the prior art and permits improvement of the frequency band characteristic, reduction in size of the device and a long-term stabilization of optical coupling efficiency.
It is another object of the present invention to provide a method for making a substrate for mounting optical components and electric circuit components thereon which substrate permits improvement of the frequency band characteristic, reduction in size of the device and a long-term stabilization of optical coupling efficiency.